1. Technical Field
The present invention relates to a thin-film transistor forming substrate, a semiconductor device, and an electric apparatus.
2. Related Art
Recently, as a general configuration of flat panel displays (FPDs) such as a liquid crystal display device, an organic EL display device, and an electrophoretic display device, a TFT active matrix is formed on a component substrate that is formed from a rigid glass substrate, and an electro-optical element (a functional element) is interposed between the component substrate and an opposing substrate. In such FPDs, there are problems of the weight, the flexibility, and the like.
As a method of forming TFT elements on a component substrate, as is disclosed in JP-A-2010-135584, a method is used in which a gate electrode, a semiconductor layer, a drain electrode, a source electrode, and the like are sequentially formed on a glass substrate. However, in accordance with the progress in miniaturization of the TFT element, in a case where the TFT element is formed by using such a technique, parasitic capacitance (electrostatic capacitance) formed between multi-layer wirings of the TFT element increases, and the power consumption increases.
In addition, generally, when the TFT element is patterned by using a printing method, the resolution is L/S=about 20/20 μm, which is quite different from the resolution L/S=3/3 μm at the time of photo-etching. The resolution of a color printer is 300 dpi, and the size of one pixel corresponds to 84 μm. Accordingly, it is difficult to realize the resolution at the time of patterning in the above-described printing method.
In addition, although it also relates to the problem of the resolution, even when the resolution is low, and the TFT elements can be formed, a space used for arranging a holding capacitor cannot be secured. Furthermore, even when the space is secured, only a holding capacitor that has low capacitance can be formed. Accordingly, in the case of an electrophoretic display device, there is a problem in that a time required for rewriting an image increases, or the power consumption increases, and in the case of a liquid crystal device, there is a problem in that flicker increases or burn-in increases.
Furthermore, in a high-precision display, the parasitic capacitance of the TFT element increases, and the resistance between wirings increases, whereby the time constant increases. Accordingly, there are problems of a decrease in the image rewriting speed, a decrease in the contrast, an increase in flicker, and the like. In a case where the TFT elements are formed on a substrate of an A4 size with the resolution of 300 dpi, about 3000×2.2 million pixels are formed, the duty ratio is 1/3000, and the number of pixels is about three times that of a general high-definition television set.
In JP-T-2010-506400, a method of manufacturing an electronic device is disclosed in which TFT elements are formed on a multi-layer substrate, and the TFT elements are formed by using wirings in the multi-layer substrate. In addition, a case is disclosed in which such an electronic device is formed as a backplane of a display device.
In JP-A-2004-004714, a configuration is disclosed in which thin film transistors are arranged on a rear face of a circuit substrate that is disposed on a side opposite to the side of an electrophoretic dispersion solution layer, and the chemical deterioration of the transistors is prevented by arranging the electrophoretic dispersion solution layer and the thin film transistors with the circuit substrate being interposed therebetween.
However, in JP-T-2010-506400, since the multi-layer substrate and a thin-film component forming layer formed from TFT elements and the like on the multi-layer substrate are formed in completely separated processes, the number of processes increases, whereby the manufacturing process is complicated. In addition, in order to allow the TFT element to have a switching function or a display image driving function, a holding capacitor needs to be formed. Accordingly, a process for forming the holding capacitors on the TFT layer is necessary, and spaces used for forming the holding capacitors are necessary, whereby it is difficult to implement high precision. In addition, generally, since the multi-layer substrate is formed from an opaque substrate, it is difficult to repair, leading to a decrease in the yield ratio, and the like so as to cause various problems.
In addition, in JP-A-2004-004714, since the thin film transistors are configured on the rear face of the circuit substrate, the thin film transistors may be easily affected by the degree of moisture or the like so as to cause a malfunction. Furthermore, there is a problem in that a blemish or the like may be included at the time of manufacturing an electro-optical device.